Gate-all-around field-effect transistor device

ABSTRACT

A method of forming a semiconductor device includes forming semiconductor strips protruding above a substrate and isolation regions between the semiconductor strips; forming hybrid fins on the isolation regions, the hybrid fins comprising dielectric fins and dielectric structures over the dielectric fins; forming a dummy gate structure over the semiconductor strip; forming source/drain regions over the semiconductor strips and on opposing sides of the dummy gate structure; forming nanowires under the dummy gate structure, where the nanowires are over and aligned with respective semiconductor strips, and the source/drain regions are at opposing ends of the nanowires, where the hybrid fins extend further from the substrate than the nanowires; after forming the nanowires, reducing widths of center portions of the hybrid fins while keeping widths of end portions of the hybrid fins unchanged, and forming an electrically conductive material around the nanowires.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyand etching techniques to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1-26 are various views of a gate-all-around (GAA) field-effecttransistor (FET) device at various stages of manufacturing, inaccordance with an embodiment.

FIG. 27 is a cross-sectional view of a GAA FET device, in accordancewith another embodiment.

FIG. 28 is a cross-sectional view of a GAA FET device, in accordancewith yet another embodiment.

FIGS. 29A and 29B together illustrate a flow chart for a method offorming a GAA FET device, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. Unless other specified, the same or similarreference numerals in different figures refer to the same or similarcomponent formed by a same or similar process(es) using a same orsimilar material(s).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In some embodiments, a gate-all-around (GAA) field-effect transistor(FET) device includes a semiconductor strip protruding above asubstrate, and a first isolation region and a second isolation region onopposing sides of the semiconductor strip. The GAA FET device alsoincludes nanowires over and aligned with the semiconductor strip, andsource/drain regions at opposing ends of the nanowires. The GAA FETdevice further includes a first dielectric fin on the first isolationregion, and a metal gate around the nanowires and around center portionsof the first dielectric fin, where end portions of the first dielectricfin are disposed on opposing sides of the metal gate, and the endportions of the first dielectric fin are wider than the center portionsof the first dielectric fin.

FIGS. 1-26 are various views (e.g., perspective view, cross-sectionalview, plan view) of a gate-all-around (GAA) field-effect transistor(FET) device 100 at various stages of manufacturing, in accordance withan embodiment. FIGS. 1-13 and 23 are perspective views of the GAA FETdevice 100. FIGS. 14-22, 25, and 26 are cross-sectional views of the GAAFET device 100, and FIG. 24 is a top view of the GAA FET device 100.Note that for clarity, some of the FIGS. 1-26 may illustrate onlyportions of, and therefore, not all, of the GAA FET device 100.

Referring to FIG. 1, a substrate 101 is provided. The substrate 101 maybe a semiconductor substrate, such as a bulk semiconductor (e.g., bulksilicon), a semiconductor-on-insulator (SOI) substrate, or the like,which may be doped (e.g., with a P-type or an N-type dopant) or undoped.The substrate 101 may be a wafer, such as a silicon wafer. Generally, anSOI substrate is a layer of a semiconductor material formed on aninsulator layer. The insulator layer may be, for example, a buried oxide(BOX) layer, a silicon oxide layer, or the like. The insulator layer isprovided on a substrate, typically a silicon or glass substrate. Othersubstrates, such as a multi-layered or gradient substrate may also beused. In some embodiments, the semiconductor material of the substrate101 includes silicon; germanium; a compound semiconductor includingsilicon carbide, gallium arsenic, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; orcombinations thereof.

In FIG. 1, an epitaxial material stack 104′ is formed over the substrate101, and a hard mask layer 107′ is formed over the epitaxial materialstack 104′. The epitaxial material stack 104′ includes alternating firstsemiconductor layers 103 and second semiconductor layers 105. The firstsemiconductor layers 103 are formed of a first semiconductor material,and the second semiconductor layers 105 are formed of a different secondsemiconductor material. In the illustrated embodiment, the firstsemiconductor material is silicon germanium (Si_(x)Ge_(1-x), where x canbe in the range of 0 to 1), and the second semiconductor material issilicon. The epitaxial material stacks 104′ may include any number oflayers. In subsequent processing, the epitaxial material stacks 104′will be patterned to form channel regions of GAA FETs. In particular,the epitaxial material stacks 104′ will be patterned to form horizontalnanowires, with the channel regions of the resulting GAA FETs includingmultiple horizontal nanowires.

The epitaxial material stacks 104′ may be formed by an epitaxial growthprocess, which may be performed in a growth chamber. During theepitaxial growth process, the growth chamber is cyclically exposed to afirst set of precursors for growing the first semiconductor layers 103,and then exposed to a second set of precursors for growing the secondsemiconductor layers 105. The first set of precursors includesprecursors for the first semiconductor material (e.g., silicongermanium), and the second set of precursors includes precursors for thesecond semiconductor material (e.g., silicon). The epitaxial materialstacks 104′ may be doped or undoped, depending on the design of the GAAFET device.

In some embodiments, the first set of precursors includes a siliconprecursor (e.g., silane) and a germanium precursor (e.g., a germane),and the second set of precursors includes the silicon precursor butomits the germanium precursor. The epitaxial growth process may thusinclude continuously enabling a flow of the silicon precursor to thegrowth chamber, and then cyclically: (1) enabling a flow of thegermanium precursor to the growth chamber when growing a firstsemiconductor layer 103; and (2) disabling the flow of the germaniumprecursor to the growth chamber when growing a second semiconductorlayer 105. The cyclical exposure may be repeated until a target numberof layers are formed. After the growth cycles are finished, aplanarization process may be performed to level the top surface of theepitaxial material stacks 104′. The planarization process may be achemical mechanical polish (CMP), an etch back process, combinationsthereof, or the like.

Next, the hard mask layer 107′ is formed over the epitaxial materialstacks 104′. The hard mask layer 107′ may include sublayers, such as apad oxide layer and an overlying pad nitride layer. The pad oxide layermay be a thin film comprising silicon oxide formed, for example, using athermal oxidation process. The pad oxide layer may act as an adhesionlayer between the epitaxial material stacks 104′ and the overlying padnitride layer. In some embodiments, the pad nitride layer is formed ofsilicon nitride, silicon oxynitride, silicon carbonitride, the like, ora combination thereof, and may be formed using low-pressure chemicalvapor deposition (LPCVD) or plasma enhanced chemical vapor deposition(PECVD), as examples.

Referring next to FIG. 2, the structure illustrated in FIG. 1 ispatterned using, e.g., photolithography and etching techniques. The hardmask layer 107′ is patterned to form a patterned hard mask 107, and thepatterned hard mask 107 is then used as an etching mask to pattern thesubstrate 101 and the epitaxial material stacks 104′. Thereafter, aliner 109 is formed over the semiconductor fins 102 and the patternedhard mask 107. Details are discussed hereinafter.

To form the semiconductor fins 102, the hard mask layer 107′ may bepatterned using photolithography techniques. Generally, photolithographytechniques utilize a photoresist material that is deposited, irradiated(exposed), and developed to remove a portion of the photoresistmaterial. The remaining photoresist material protects the underlyingmaterial, such as the hard mask layer 107′ in this example, fromsubsequent processing steps, such as etching. In this example, thephotoresist material is used to pattern the hard mask layer 107′ to formthe patterned hard mask 107, as illustrated in FIG. 2.

The patterned hard mask 107 is subsequently used to pattern thesubstrate 101 and the epitaxial material stack 104′ to form trenches108, thereby defining semiconductor fins 102 between adjacent trenches108, as illustrated in FIG. 2. In the illustrated embodiment, each ofthe semiconductor fins 102 includes a semiconductor strip 106 and apatterned epitaxial material stack 104 over the semiconductor strip 106.The semiconductor strip 106 is a patterned portion of the substrate 101and protrudes above the (recessed) substrate 101. The patternedepitaxial material stack 104 is a patterned portion of the epitaxialmaterial stack 104′ and will be used to form nanowires in subsequentprocessing, and therefore, may also be referred to as nanowirestructures 104 or GAA structures 104.

In some embodiments, the semiconductor fins 102 are formed by etchingtrenches in the substrate 101 and in the epitaxial material stack 104′using, for example, reactive ion etch (RIE), neutral beam etch (NBE),the like, or a combination thereof. The etching process may beanisotropic. In some embodiments, the trenches 108 may be strips (viewedfrom in the top) parallel to each other, and closely spaced with respectto each other. In some embodiments, the trenches 108 may be continuousand surround the semiconductor fins 102. The semiconductor fins 102 mayalso be referred to as fins 102 hereinafter.

The fins 102 may be patterned by any suitable method. For example, thefins 102 may be patterned using one or more photolithography processes,including double-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers, or mandrels, may then be usedto pattern the fins.

After the fins 102 are formed, the liner 109 is formed along sidewallsand bottoms of the trenches 108. The liner 109 may also be formed overthe upper surfaces of the patterned hard mask 107. In an exampleembodiment, the liner 109 is a silicon liner formed by, e.g., CVD,atomic layer deposition (ALD), combinations thereof, or the like.

FIG. 3 illustrates the formation of an insulation material betweenneighboring semiconductor fins 102 to form isolation regions 111. Theinsulation material may be an oxide, such as silicon oxide, a nitride,the like, or a combination thereof, and may be formed by a high densityplasma chemical vapor deposition (HDP-CVD), a flowable CVD (FCVD) (e.g.,a CVD-based material deposition in a remote plasma system and postcuring to make it convert to another material, such as an oxide), thelike, or a combination thereof. Other insulation materials and/or otherformation processes may be used. In the illustrated embodiment, theinsulation material is silicon oxide formed by a FCVD process. An annealprocess may be performed once the insulation material is formed. Aplanarization process, such as CMP, may remove any excess insulationmaterial from over the top surfaces of the semiconductor fins 102.

Next, the isolation regions are recessed to form shallow trenchisolation (STI) regions 111. The isolation regions 111 are recessed suchthat the upper portions of the semiconductor fins 102 protrude frombetween neighboring STI regions 111. The top surfaces of the STI regions111 may have a flat surface (as illustrated), a convex surface, aconcave surface (such as dishing), or a combination thereof. The topsurfaces of the STI regions 111 may be formed flat, convex, and/orconcave by an appropriate etch. The isolation regions 111 may berecessed using an acceptable etching process, such as one that isselective to the material of the isolation regions 111. For example, adry etch, or a wet etch using dilute hydrofluoric (dHF) acid, may beperformed to recess the isolation regions 111. In FIG. 3, the uppersurface of the STI regions 111 is illustrated to be level with uppersurfaces of the semiconductor strips 106. In other embodiments, theupper surface of the STI regions 111 is lower (e.g., closer to thesubstrate 101) than the upper surfaces of the semiconductor strips 106.

Next, in FIG. 4, a capping layer 113 is conformally formed over the GAAstructure 104 and over the patterned hard mask 107. The capping layer113 is an epitaxial semiconductor layer formed using, e.g., a CVDprocess, in some embodiments. In an example embodiment, the cappinglayer 113 and the first semiconductor layer 103 are formed of a sameepitaxial material, such as silicon germanium. The capping player 113 isselectively grown on exposed surfaces of the liner 109 (e.g., a siliconliner, see FIG. 3) using an epitaxial growth process, and therefore, theupper surface of the STI region 111 is free of the capping layer 113, insome embodiments. The capping layer 113 may have a thickness of about 5nm, as an example. To avoid clutter, portions of the liner 109 disposedabove the upper surface of the STI regions 111 are not illustrated inFIG. 4 and subsequent figures, with the understanding that the liner 109may exist between the capping layer 113 and the GAA structure104/patterned hard mask 107.

Next, in FIG. 5, a dielectric layer 114 is conformally formed over thecapping layer 113 and over the upper surface of the STI regions 111.Next, a dielectric layer 115 is formed over the dielectric layer 114 tofill the trenches 108. The dielectric layer 114 and the dielectric layer115 are then etched back to form dielectric fins 116, details of whichare discussed hereinafter.

In some embodiments, the dielectric layer 114 is formed by forming aconformal layer of silicon nitride along the capping layer 113 and alongthe upper surface of the STI regions 111 using a suitable depositionmethod such as CVD. The dielectric layer 115 is then formed over thedielectric layer 114. In the illustrated embodiment, the dielectriclayer 115 is formed using a low-K dielectric material (e.g., having adielectric constant K smaller than about 7, such as smaller than about3.9), such as SiO₂, SiN, SiCN, or SiOCN.

Next, the dielectric layer 115 (e.g., a low-K dielectric material) isetched back using, e.g., a dry etch process or a wet etch process. Forexample, a dry etch process using a fluoride-containing gas may be usedto etch back the dielectric layer 115. After the dielectric layer 115 isetched back, the dielectric layer 114 exposed by the recessed dielectriclayer 115 is removed by a suitable etching process, such as a dry etchprocess or a wet etch process. For example, a wet etch process usingH₃PO₄ as etchant may be performed to remove the exposed dielectric layer114. The remaining portions of the dielectric layer 114 and theremaining portions of the dielectric layer 115 form the dielectric fins116. In the example of FIG. 5, the upper surface of the remainingportions of the dielectric layer 114 and the upper surface of theremaining portions of the dielectric layer 115 are level with eachother. Since both the dielectric layer 114 and the dielectric layer 115are formed of low-K dielectric materials, the dielectric fins 116 mayalso be referred to as low-K dielectric fins. As illustrated in FIG. 5,the dielectric fins 116 are formed on the STI regions 111, andphysically contact the capping layer 113 disposed on opposing sides ofthe dielectric fins 116.

Next, in FIG. 6, dielectric structures 118 are formed to fill remainingportions of the trenches 108. In the example of FIG. 6, the dielectricstructures 118 are formed by conformally forming a dielectric layer 117over the structure of FIG. 5, and thereafter, forming a dielectric layer119 over the dielectric layer 117. A planarization process, such as CMP,is then performed to remove portions of the capping layer 113, portionsof the dielectric layer 117, and portions of the dielectric layer 119from the upper surface of the patterned hard mask 107.

In some embodiments, the dielectric layer 117 is formed of aluminumoxide (e.g., AlO_(x)) using a suitable deposition method such as CVD,PVD, combinations thereof, or the like. A thickness of the dielectriclayer 117 may be, e.g., about 2 nm. The dielectric layer 119 is formedof a high-K dielectric material (e.g., having a dielectric constant Klarger than about 7), such as HfO₂, ZrO₂, HfAlO_(x), HfSiO_(x), orAl₂O₃, as examples. Since the dielectric layer 117 and the dielectriclayer 119 are both formed of high-K dielectric materials, the dielectricstructure 118 may also be referred to as a high-K dielectric structure.In addition, since the dielectric fins 116 are formed of low-Kdielectric materials, and since the dielectric structures 118 are formedof high-K dielectric materials, each dielectric fins 116 and arespective overlying dielectric structures 118 may be collectivelyreferred to as a hybrid fin 112.

Referring next to FIG. 7, dummy gate structures 122 are formed over thesemiconductor fins 102 (see label in FIG. 6) and over the hybrid fins112. Each of the dummy gate structures 122 includes a gate dielectric121 and a gate electrode 123, in some embodiments.

To form the dummy gate structure 122, a dielectric layer is formed onthe structure illustrated in FIG. 6. The dielectric layer may be, forexample, silicon oxide, silicon nitride, multilayers thereof, or thelike, and may be deposited or thermally grown. Next, a gate layer isformed over the dielectric layer, and a mask layer is then formed overthe gate layer. The gate layer may be deposited over the dielectriclayer and then planarized, such as by a CMP process. The mask layer maybe deposited over the gate layer. The gate layer may be formed of, forexample, polysilicon, although other materials may also be used. Themask layer may be formed of, for example, silicon oxide, siliconnitride, combinations thereof, or the like.

After the layers (e.g., the dielectric layer, the gate layer, and themask layer) are formed, the mask layer may be patterned using acceptablephotolithography and etching techniques to form mask 126. In the exampleof FIG. 7, the mask 126 includes a first mask 125 (e.g., silicon oxide)and a second mask 127 (e.g., silicon nitride). The pattern of the mask126 is then transferred to the gate layer and the dielectric layer by anacceptable etching technique to form the gate electrode 123 and the gatedielectric 121, respectively. The gate electrode 123 and the gatedielectric 121 are over (e.g., directly over) the respective channelregions of the GAA FET device to be formed. The gate electrode 123 mayalso have a lengthwise direction substantially perpendicular to thelengthwise direction of the semiconductor fins 102 or the lengthwisedirection of the hybrid fins 112.

Next, in FIG. 8, gate spacers 129 are formed over sidewalls of the gateelectrode 123 and the gate dielectric 121. The gate spacer 129 may beformed by conformally depositing a gate spacer layer over the structureillustrated in FIG. 7. The gate spacer layer may be silicon nitride,silicon carbonitride, a combination thereof, or the like. In someembodiments, the gate spacer layer includes multiple sublayers. Forexample, a first sublayer (sometimes referred to as a gate seal spacerlayer) may be formed by thermal oxidation or a deposition, and a secondsublayer (sometimes referred to as a main gate spacer layer) may beconformally deposited on the first sublayer. The gate spacers 129 areformed by anisotropically etching the gate spacer layer. The anisotropicetching may remove horizontal portions of the gate spacer layer (e.g.,over the patterned hard mask 107, the hybrid fins 112, and the mask126), with remaining vertical portions of the gate spacer layer (e.g.,along sidewalls of the gate electrode 123 and sidewalls of the gatedielectric 121) forming the gate spacers 129. In the discussion herein,the gate spacers 129 may also be referred to as part of the dummy gatestructure 122.

Next, an anisotropic etching process is performed to remove portions ofthe dielectric structure 118, portions of the GAA structures 104 (e.g.,103 and 105), and portions of the patterned hard mask 107 that areoutside the boundaries of the dummy gate structure 122 (e.g., outsidethe exterior sidewalls of the gate spacers 129). The anisotropic etchingprocess may be performed using the dummy gate structure 122 as anetching mask. After the anisotropic etching, the sidewall 129S of thegate spacer 129 is aligned with a respective sidewall 105S of the secondsemiconductor layer 105, due to the anisotropic etching, in someembodiments.

In some embodiments, the anisotropic etching process is a dry etchprocess (e.g., a plasma etch process) using an etchant(s) that isselective to (e.g., having a higher etching rate for) the materials ofthe patterned hard mask 107 and the GAA structure 104. In an exampleembodiment, the dry etch process has an average etching rate of E₁ forthe dielectric structure 118 (e.g., high-K material) and an averageetching rate of E₂ (E₂>E₁) for the combination of the patterned hardmask 107 (e.g., low-K material) and the GAA structure 104 (e.g.,semiconductor material), and the ratio between E₁ and E₂ may be chosento be E₁/E₂=H₁/H₂, where H₁ is the height of the dielectric structure118, and H₂ is the sum of the height of the patterned hard mask 107 andthe height of the GAA structure 104. With the above relationship betweenthe ratios, when the dielectric structure 118 (e.g., outside theboundaries of the dummy gate structure 122) is removed to expose theunderlying dielectric fin 116, at the same time, the patterned hard mask107 and the GAA structure 104 (e.g., outside the boundaries of the dummygate structure 122) are also removed to expose the underlyingsemiconductor strips 106.

Next, in FIG. 9, a lateral etching process is performed to recessexposed portions of the first semiconductor material using an etchantthat is selective to the first semiconductor material. In the example ofFIG. 9, both the capping layer 113 and the first semiconductor layer 103are formed of the first semiconductor material (e.g., SiGe), andtherefore, the lateral etch recesses both the capping layer 113 and thefirst semiconductor layer 103. After the lateral etching process, thefirst semiconductor material is recessed from the sidewalls 129S of thegate spacers 129, from the sidewalls 105S of the (remaining portions of)second semiconductor layer 105, and from the sidewalls of the (remainingportions of) patterned hard mask 107. For example, FIG. 9 illustrates anoffset R between the sidewall 105S of the second semiconductor layer 105and the sidewall of the recessed first semiconductor layer 103.

Next, in FIG. 10, a dielectric material 131 is formed to fill the spaceleft by the removal (e.g., recess) of the first semiconductor materialdiscussed above with reference to FIG. 9. The dielectric material 131may be a low-K dielectric material, such as SiO₂, SiN, SiCN, or SiOCN,and may be formed by a suitable deposition method, such as ALD. Afterthe deposition of the dielectric material 131, an anisotropic etchingprocess may be performed to trim the deposited dielectric material 131,such that only portions of the deposited dielectric material 131 thatfill the space left by the removal of the first semiconductor materialare left. After the trimming process, the remaining portions of thedeposited dielectric material 131 form inner spacers 131. The innerspacers 131 serve to isolate metal gates from source/drain regionsformed in subsequent processing. In the example of FIG. 9, frontsidewalls of the inner spacers 131 are aligned with the sidewall 129S ofthe gate spacers 129.

Next, in FIG. 11, source/drain regions 133 are formed over thesemiconductor strips 106. The source/drain regions 133 are formed byepitaxially growing a material over the semiconductor strips 106, usingsuitable methods such as metal-organic CVD (MOCVD), molecular beamepitaxy (MBE), liquid phase epitaxy (LPE), vapor phase epitaxy (VPE),selective epitaxial growth (SEG), the like, or a combination thereof.

As illustrated in FIG. 11, the epitaxial source/drain regions 133 fillthe spaces between adjacent dielectric fins 116. The epitaxialsource/drain regions 133 may have surfaces raised from surfaces of thedielectric fins 116 and may have facets. The source/drain regions 133over adjacent semiconductor strips 106 may merge to form a continuousepitaxial source/drain region 133, as illustrated in FIG. 11. In someembodiments, the source/drain regions 133 over adjacent semiconductorstrips 106 do not merge together and remain separate source/drainregions 133. The material(s) of the source/drain regions 133 may betuned in accordance with the type of devices to be formed. In someembodiments, the resulting GAA FET is an n-type FinFET, and source/drainregions 133 comprise silicon carbide (SiC), silicon phosphorous (SiP),phosphorous-doped silicon carbon (SiCP), or the like. In someembodiments, the resulting GAA FET is a p-type FinFET, and source/drainregions 133 comprise SiGe, and a p-type impurity such as boron orindium.

The epitaxial source/drain regions 133 may be implanted with dopantsfollowed by an anneal process. The implanting process may includeforming and patterning masks such as a photoresist to cover the regionsof the GAA FET device that are to be protected from the implantingprocess. The source/drain regions 133 may have an impurity (e.g.,dopant) concentration in a range from about 1E19 cm⁻³ to about 1E21cm⁻³. P-type impurities, such as boron or indium, may be implanted inthe source/drain region 133 of a P-type transistor. N-type impurities,such as phosphorous or arsenide, may be implanted in the source/drainregions 133 of an N-type transistor. In some embodiments, the epitaxialsource/drain regions may be in situ doped during growth.

Next, in FIG. 12, a contact etch stop layer (CESL) 135 is formed overthe structure illustrated in FIG. 11, and an interlayer dielectric (ILD)layer 137 is formed over the CESL 135. The CESL 135 functions as an etchstop layer in a subsequent etching process, and may comprise a suitablematerial such as silicon oxide, silicon nitride, silicon oxynitride,combinations thereof, or the like, and may be formed by a suitableformation method such as CVD, PVD, combinations thereof, or the like.

The ILD layer 137 is formed over the CESL 135 and around the dummy gatestructures 122. In some embodiments, the ILD layer 137 is formed of adielectric material such as silicon oxide, phosphosilicate glass (PSG),borosilicate glass (BSG), boron-doped phosphosilicate Glass (BPSG),undoped silicate glass (USG), or the like, and may be deposited by anysuitable method, such as CVD, PECVD, or FCVD. A planarization process,such as a CMP process, may be performed to remove the mask 126 (see FIG.11) and to remove portions of the CESL 135 disposed over the gateelectrode 123. As illustrated in FIG. 12, after the planarizationprocess, the top surface of the ILD layer 137 is level with the topsurface of the gate electrode 123.

Next, in FIG. 13, the gate electrode 123 (see FIG. 12) and the gatedielectric 121 (see FIG. 12) of the dummy gate structure are removed inan etching step(s), so that recesses 128 are formed between the gatespacers 129. Each recess exposes the remaining portions of the patternedhard mask 107 that are disposed under the dummy gate structure. Afterthe removal of the gate electrode 123 and the gate dielectric 121, cutmetal gate (CMG) patterns 139 are formed in the recesses 128. Topsurfaces of the CMG patterns 139 may extend above the upper surface ofthe ILD layer 137. The CMG patterns 139 may be formed by depositing aphotoresist layer in the recesses 128, forming a patterned hard masklayer 139A (see FIG. 14) over the photoresist layer, and forming apatterned photoresist 139B by patterning the photoresist layer using thepatterned hard mask layer 139A.

FIGS. 14-22 illustrate cross-sectional views of the GAA FET device 100at various stages of processing along cross-section B-B in FIG. 13,where the cross-section B-B is between the gate spacers 129 (e.g., inthe recess 128) and along a longitudinal direction of the dummy gatestructures 122. FIG. 14 illustrates the cross-sectional view of the GAAFET device 100 along the cross-section B-B after the CMG patterns 139are formed, as descried above with reference to FIG. 13.

Next, in FIG. 15, dielectric structures 118 that are exposed by the CMGpatterns 139 are removed, e.g., by an etching process. The etchingprocess may use an etchant that is selective to the materials of thedielectric structures 118. For example, a dry etch process using achlorine-containing etchant may be performed to remove the exposeddielectric structures 118. After the dielectric structures 118 areremoved, the CMG patterns 139 are removed by a suitable method, such asan etching process, an ashing process, combinations thereof, or thelike. Recesses 136 are formed at places where the removed dielectricstructures 118 used to be.

Referring next to FIG. 16, the upper surface of the patterned hard mask107 is recessed, e.g., by a dry etch process, such that the uppersurface of the patterned hard mask 107 is below (e.g., closer to thesubstrate 101) the upper surface of the dielectric structure 118. Theupper surface of the capping layer 113 may also be recessed by theetching process. In the example of FIG. 16, a residue portion of thepatterned hard mask 107 remains after the etching process. In subsequentprocessing, the residue portion of the patterned hard mask 107 mayprotect the underlying nanowires 110 (see FIGS. 17-19) from being overetched by subsequent etching process(es). In other embodiments, thepatterned hard mask 107 is completely removed (see, e.g., FIG. 27) bythe etching process.

Next, in FIG. 17, the first semiconductor layers 103 and the cappinglayer 113 are removed to release the second semiconductor layer 105,such that the center portions (e.g., portions between inner spacers 131and under the recess 128) of the second semiconductor layers 105 aresuspended. After the first semiconductor layers 103 and the cappinglayer 113 are removed, the second semiconductor layer 105 forms aplurality of nanowires 110. In other words, the second semiconductorlayer 105 may also be referred to as nanowires 110 in subsequentprocessing.

Since the first semiconductor layers 103 and the capping layer 113 areboth formed of the first semiconductor material (e.g., SiGe), aselective etching process, such as a dry etch or a wet etch that isselective to the first semiconductor material may be performed to formthe nanowires 110. The selective etching process to remove the firstsemiconductor material may also slightly etch the second semiconductorlayer 105, which may recess the sidewalls of the second semiconductorlayer 105 by, e.g., about 0.5 nm on each side (e.g., left side and rightside in FIG. 17), which increases the distance D (see FIG. 18) betweenthe nanowires 110 and the dielectric fins 116, details of which aredescribed hereinafter.

Note that the center portions of the nanowires 110 are suspended, withempty spaces 134 between adjacent nanowires 110 and between thedielectric fins 116 and the nanowires 110. Other portions (may bereferred to as end portions) of the nanowires 110, e.g. portions underthe gate spacers 129 and portions beyond the boundaries of the gatespacers 129, are not released by the selective etching process describedabove. Instead, the nanowires 110 are surrounded by the inner spacer131, as described below with reference to FIG. 25.

Next, in FIG. 18, the dielectric layer 117 (e.g., aluminum oxide)disposed along the sidewalls of the dielectric layer 119 is removed byan etching process. For example, a wet etch process using a mixture ofhydrogen peroxide (H₂O₂) and ammonia (NH₃) may be performed to removethe dielectric layer 117. Portions of the dielectric layer 117 under thedielectric layer 119 remain after the etching process, as illustrated inFIG. 18.

In addition, the dielectric layer 114 (e.g., a silicon nitride layer)disposed along the sidewalls of the dielectric layer 115 is removed byan etching process. For example, a wet etch process using H₃PO₄ may beperformed to remove the dielectric layer 114. As illustrated in FIG. 18,portions of the dielectric layer 114 under the dielectric layer 115remain after the etching process.

After the removal of the sidewall portions of the dielectric layer 117and the sidewall portions of the dielectric layer 114, the thickness T₁of the dielectric fin 116 is reduced (e.g., by about 1 nm on the leftside and about 1 nm on the right side in FIG. 18), which results in anincrease in the distance D between the dielectric fin 116 and adjacentnanowires 110. The increased distance D facilitates the metal fillingprocess to form the gate electrode 143 (see FIG. 21) in subsequentprocessing, which illustrates an advantage of the present disclosure. Asfeatures sizes continue to shrink in advanced processing nodes, thewidth of the recess 128 (see FIG. 13) between the gate spacers 129 aregetting increasingly small, making it difficult to fill the recess 128with a conductive material to form the gate electrodes 143. A poorlyfilled recess 128 may decrease production yield, and/or increase theelectrical resistance of the metal gate formed. By increasing thedistance D, the current disclosure makes it easier to fill the recess128, thereby improving the production yield and reduces the electricalresistance of the metal gate formed. In addition, since the increaseddistance D allows for easy fill of the fill metal, a smaller spacing S(e.g., between about 20 nm and about 40 nm) between adjacentsemiconductor strips 106 is made possible by the present disclosure,which advantageously reduces the size (e.g., cell height) of the deviceformed and increases the integration density of the device.

Next, in FIG. 19, an optional hybrid fin trimming process is performedto further reduce the width of the hybrid fin 112 (e.g., the width T₁ ofthe dielectric fin 116, which may be the same as the width of thedielectric structure 118), and to further increase the distance D. Thehybrid fin trimming process may be any suitable etching process, such asa dry etch or a wet etch. In some embodiments, the hybrid fin trimmingprocess is omitted.

Referring next to FIG. 20, an interface layer 142 is formed over thesurfaces of the nanowires 110. The interface layer 142 is a dielectriclayer, such as an oxide, and may be formed by a thermal oxidizationprocess or a deposition process. In the illustrated embodiment, athermal oxidization process is performed to convert exterior portions ofthe nanowires 110 into an oxide to form the interface layer 142, and asa result, the interface layer 142 is not formed over the dielectric fins116 or the dielectric structures 118.

After the interface layer 142 is formed, a gate dielectric layer 141 isformed around the nanowires 110, on the dielectric fins 116, on thedielectric structures 118, and on the patterned hard mask 107. The gatedielectric layer 141 is also formed on the upper surface of the STIregions 111, as illustrated in FIG. 20. In some embodiments, the gatedielectric layer 141 includes a high-k dielectric material (e.g., havinga K value greater than about 7.0), and may include a metal oxide or asilicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, or combinations thereof. Forexample, the gate dielectric layers 141 may comprise HfO₂, ZrO₂,HfAlO_(x), HfSiO_(x), Al₂O₃, or combinations thereof. The formationmethods of the gate dielectric layer 141 may include molecular beamdeposition (MBD), ALD, PECVD, and the like.

In the example of FIG. 20, portions of the gate dielectric layer 141formed around the nanowires 110 merge with adjacent gate dielectriclayers 141. As a result, the gate dielectric layer 141 completely fillsthe gaps between vertically adjacent nanowires 110, and fills the gapsbetween the topmost nanowires 110 and the respective overlying patternedhard mask 107. In addition, the gate dielectric layers 141 completelyfills the gaps between the bottommost nanowires 110 and the underlyingsemiconductor strips 106, as illustrated in FIG. 20. In someembodiments, the merged gate dielectric layers 141 may preventover-etching of gate electrode 143 (see FIG. 22) in a subsequent etchingprocess. In other embodiments, the portions of the gate dielectric layer141 around the nanowires 110 do not merge, and therefore, thesubsequently formed gate electrode fills the gaps between, e.g.,vertically adjacent nanowires 110, as illustrated in the embodiment ofFIG. 28.

Next, in FIG. 21, an electrical conductive material (may also bereferred to as a fill metal) is formed in the recess 128 to form gateelectrode 143. The gate electrode 143 may be made of a metal-containingmaterial such as Cu, Al, W, the like, combinations thereof, ormulti-layers thereof, and may be formed by, e.g., electroplating,electroless plating, or other suitable method. After the gate electrode143 is formed, a planarization process such as CMP may be performed toplanarize the upper surface of the gate electrode 143.

Although not illustrated, barrier layers and work function layers may beformed over the gate dielectric layer 141 and around the nanowires 110before the electrical conductive material is formed. The barrier layermay comprise an electrically conductive material such as titaniumnitride, although other materials, such as tantalum nitride, titanium,tantalum, or the like, may alternatively be utilized. The barrier layermay be formed using a CVD process, such as PECVD. However, otheralternative processes, such as sputtering, metal organic chemical vapordeposition (MOCVD), or ALD, may alternatively be used. After the barrierlayer is formed, the work function layer is formed over the barrierlayer, in some embodiments.

In the example of FIG. 21, the GAA FET device has an N-type deviceregion 510 and a P-type device region 520. Therefore, an N-type workfunction layer may be formed over the barrier layer and around thenanowire 110 in the N-type device region 510, and a P-type work functionlayer may be formed over the barrier layer and around the nanowire 110in the P-type device region 520. Exemplary P-type work function metalsthat may be included in the gate structures for P-type devices includeTiN, TaN, Ru, Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, other suitableP-type work function materials, or combinations thereof. ExemplaryN-type work function metals that may be included in the gate structuresfor N-type devices include Ti, Ag, TaAl, TaAlC, TiAlN, TaC, TaCN, TaSiN,Mn, Zr, other suitable N-type work function materials, or combinationsthereof. A work function value is associated with the materialcomposition of the work function layer, and thus, the material of thework function layer is chosen to tune its work function value so that atarget threshold voltage Vt is achieved in the device that is to beformed. The work function layer(s) may be deposited by CVD, physicalvapor deposition (PVD), and/or other suitable process.

To form the different work function layers in the N-type device region510 and the P-type device region 520, a patterned mask layer, such as apatterned photoresist, may be formed to cover a first region (e.g., 510)while the work function layer is being formed in the second region(e.g., 520) exposed by the patterned mask layer. Next, the fill metalmay be formed over the work function layer in the second region (e.g.,520) to form gate electrode 143P (e.g., portion of the gate electrode143 that is in the region 520). Similar process may be repeated to coverthe second region (e.g., 520) while the work function layer is formed inthe first region (e.g., 510), and the fill metal may be formed in thefirst region over the work function layer to form gate electrode 143N(e.g., portion of the gate electrode 143 that is in the region 510). Inthe example of FIG. 21, there is an interface 144 between the gateelectrodes 143N and 143P, where the barrier layer and the work functionlayers may extend along the interface 144. For example, an N-type workfunction layer may extend along the left side of the interface 144, anda P-type work function layer may extend along the right side of theinterface 144. In other embodiments, the fill metal may be formed inboth the N-type device region 510 and the P-type device region 520 in asingle step after the N-type work function layer and the P-type workfunction layer are formed, in which case the interface 144 may not beformed.

Next, in FIG. 22, the gate electrode 143 is recessed below the uppersurface of the dielectric structure 118 (e.g., the upper surface of thedielectric layer 119). An etching process that is selective to thematerial (e.g., metal) of the gate electrode 143 may be performed toremove top layers of the gate electrode 143 without substantiallyattacking the dielectric layer 119. In the example of FIG. 22, after thegate electrode 143 is recessed, the dielectric structures 118 separatethe gate electrode 143 into three separate portions, and therefore,three separate gate structures 145 (e.g., 145A, 145B, and 145C) areformed in a self-aligned manner, where each of the gate structures 145includes the gate dielectric layer 141, the barrier layer, at least onework function layer, and the gate electrode 143. In the example of FIG.22, the gate structure 145A is formed in the N-type device region 510and has an N-type work function layer. The gate structure 145C is formedin the P-type device region 520 and has a P-type work function layer.The gate structure 145B, however, has its left portion (e.g., left ofthe interface 144) in the N-type device region 510 and its right portion(e.g., right of the interface 144) in the P-type device region 520, andtherefore, the work function layer of the gate structure 145B includes aleft portion formed of an N-type work function layer and includes aright portion formed of a P-type work function layer.

The self-aligned metal gate formation method disclosed herein providesadvantages compared with a reference cut metal gate (CMG) process, wherethe gate electrode 143 is cut into separate metal gates by formingopenings in the gate electrode 143 and filling the opening with adielectric material. For advanced processing nodes, the reference CMGprocess may have difficulty filling the openings, due to the high aspectratio of the openings. Poorly filled openings may cause electricalshorts between the gate structures and may cause device failure. Thecurrent disclosure allows for easy separation of the metal gates in aself-aligned manner, thus preventing device failure and improvingproduction yield.

After the gate structures 145 are formed, an etch stop layer 147 isformed (e.g., selectively formed) over the gate electrode 143. In someembodiments, the etch stop layer 147 is a fluorine-free tungsten (FFW)layer. The etch stop layer 147 (e.g., tungsten) may act as an etch stoplayer in a subsequent etching process, and in addition, may help toreduce the electrical resistance of the gate structures 145 and/or gatecontact plugs formed thereafter. After the etch stop layer 147 isformed, a dielectric layer 149 is formed over the etch stop layer 147.In some embodiments, a planarization process is performed to planarizethe upper surface of the dielectric layer 149.

In the example of FIG. 22, the height H₃ of the dielectric layer 119 ofthe dielectric structure 118 is between about 10 nm and about 40 nm, andthe dielectric layer 119 extends above the upper surface of the etchstop layer 147 by a distance H₄, which is larger than about 4 nm. Therange of the distance H₄ ensures a safety margin large enough to avoidelectrical short between adjacent gate structures 145, which electricalshort may happen if the upper surface of the dielectric layer 119 isbelow the upper surface of the gate electrode 143.

FIG. 23 illustrates a perspective view of the GAA FET device 100 afterthe processing illustrated in FIG. 22. In FIG. 23, the patterned hardmask 107 has a U-shaped cross-section, which is due to the anisotropicetch to recess the patterned hard mask 107 discussed above withreference to FIG. 16. The anisotropic etch also removes top portions ofthe gate spacers 129 and results in a reduced height for the gatespacers 129, as shown in FIG. 23. Since the interface layer 142surrounds the nanowires 110, the locations of the interface layer 142 inFIG. 23 correspond to locations of the nanowires 110 (as indicated bythe label 142/110). FIG. 23 further illustrates the inner spacers 131disposed under the gate spacers 129. Source/drain regions 133 areconnected to opposing ends of the nanowires 110, as illustrated in FIG.23.

FIG. 24 illustrates a plan view of the GAA FET device 100 of FIGS. 22and 23. For clarity, not all features are illustrated. FIG. 24illustrates the semiconductor strips 106, the gate electrodes 143, andthe gate spacers 129. Cross-section B-B (see also FIG. 13) is along alongitudinal direction of the gate electrode 143 and across the gateelectrode 143. Cross-section A-A (see also FIG. 10) is parallel tocross-section B-B, but across the gate spacer 129. Cross-section C-C(see also FIG. 13) is parallel to cross-section B-B, but between twoadjacent gate structures and across the source/drain regions 133 (notillustrated in FIG. 24).

FIG. 25 illustrates a cross-sectional view of the GAA FET device 100 ofFIGS. 22 and 23, but along cross-section A-A. Note that in thecross-sectional view of FIG. 25, portions of the nanowires 110 disposedunder (e.g., directly under) the gate spacers 129 are surrounded by theinner spacer 131. In contrast, referring to FIG. 22, portions of thenanowires 110 under the gate electrode 143 (e.g., between a pair of gatespacers 129) is surrounded by the gate dielectric layer 141 and theinterface layer 142. The nanowires 110 are also at least partiallysurrounded by the gate electrode 143. In addition, in the embodiment ofFIG. 28, the nanowires 110 are fully surrounded (e.g., in a full circle)by the gate electrode 143.

FIG. 26 illustrates a cross-section of the GAA FET device 100 alongcross-section C-C, after source/drain contacts 151 are formed, followingthe processing of FIGS. 22 and 23. Source/drain contacts 151 may beformed by forming openings in the ILD layer 137 to expose the underlyingsource/drain regions 133, forming silicide regions 153 over thesource/drain regions 133, and filling the openings with an electricallyconductive material (e.g., Cu, W, Co, Al).

The openings for the source/drain contacts 151 may be formed byperforming a photolithography and etching process to etch through theCESL 135 to expose the source/drain regions 133. The silicide regions153 may be formed by first depositing a metal capable of reacting withsemiconductor materials (e.g., silicon, germanium) to form silicide orgermanide regions, such as nickel, cobalt, titanium, tantalum, platinum,tungsten, other noble metals, other refractory metals, rare earth metalsor their alloys, over the exposed portions of the source/drain regions133, then performing a thermal anneal process to form the silicideregions 153. The un-reacted portions of the deposited metal are thenremoved, e.g., by an etching process. Next, a barrier layer may beformed lining sidewalls and bottoms of the openings in the ILD layer137, and thereafter, a fill metal is formed to fill the openings.Additional processing may be performed after the processing of FIG. 26to finish the GAA FET device 100, as one skilled in the art readilyappreciates, thus details are not discussed here.

Note that in FIG. 26, the width of the dielectric fin 116 beyondboundaries of the gate structure 145 (e.g., directly under thesource/drain regions 133) is T₂, which is larger than the width T₁ (seeFIGS. 18 and 19) of the dielectric fin 116 under (e.g., directly under)the gate electrode 143. In some embodiments, the difference between T₂and T₁ is between about 2 nm and about 20 nm.

The larger width T₂ of the dielectric fin 116 under the source/drainregion 133 allows for larger error tolerance (or less stringentrequirement) for the photolithography and etching process. For example,if the source/drain contacts 151 are shifted (e.g., to the left side orto the right side) due to inaccuracy in the photolithography and etchingprocess to form the contact openings, the larger width T₂ of thedielectric fin 116 can tolerate a large amount of shift beforeelectrical short happens between two adjacent source/drain regions 133(e.g., 133A and 133B in FIG. 26). As another example, consider thedoping (e.g., the implanting process) of the source/drain regions 133 indifferent regions (e.g., N-type device region 510 and P-type deviceregion 520) for different types (e.g., N-type, or P-type) oftransistors, where a patterned mask may be used to cover thesource/drain regions 133 in one region (e.g., 510) while exposinganother region (e.g., 520) for doping. The larger width T₂ allows forlarger error margins for the boundary of the mask layer, which boundarymay be on the top surface of the dielectric fins 116. In addition, thelarger width T₂ of the dielectric fin 116 reduces or prevents bridgingof adjacent source/drain regions (e.g., bridging between source/drainregions 133A and 133B). Furthermore, the larger width T₂ of thedielectric fin 116 improve the time dependent dielectric breakdown(TDDB) performance (e.g., from source/drain contact 151A to source/drainregion 133B, or from source/drain contact 151B to source/drain region133A) of the device formed. On the other hand, the smaller width T₁ (seeFIGS. 18 and 19) of the dielectric fin 116 under the gate electrode 143allows for easy fill of the recess 128 by the fill metal, thus improvingproduction yield and reducing the electrical resistance of the gatestructures formed.

Modifications or variations to the disclosed embodiment are possible andare fully intended to be included within the scope of the presentdisclosure. A few examples are illustrated in FIGS. 27 and 28. FIG. 27is a cross-sectional view of a GAA FET device 100A, in accordance withanother embodiment. The GAA FET device 100A is similar to the GAA FETdevice 100 in FIG. 22, but with the patterned hard mask 107 (see, e.g.,FIG. 22) completely removed.

FIG. 28 is a cross-sectional view of a GAA FET device 100B, inaccordance with yet another embodiment. The GAA FET device 100B issimilar to the GAA FET device 100A in FIG. 27, but the gate dielectriclayer 141 around vertically adjacent nanowires 110 does not merge.Instead, the gaps between vertically adjacent nanowires 110 are filledby the fill metal of the gate electrode 143. Similarly, the fill metalof the gate electrode 143 fills gaps between the bottommost nanowires110 and the semiconductor strips 106.

FIGS. 29A and 29B together illustrate a flow chart for a method offorming a GAA FET device, in accordance with some embodiments. It shouldbe understood that the embodiment method shown in FIGS. 29A and 29B ismerely an example of many possible embodiment methods. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. For example, various steps as illustrated in FIGS. 29Aand 29B may be added, removed, replaced, rearranged and repeated.

Referring to FIGS. 29A and 29B, at step 1010, semiconductor fins areformed over a substrate and a patterned mask layer is formed over thesemiconductor fins, where the semiconductor fins comprise epitaxiallayers over semiconductor strips, where the epitaxial layers comprisealternating layers of a first semiconductor material and a secondsemiconductor material. At step 1020, hybrid fins are formed overisolation regions on opposing sides of the semiconductor fins, whereeach of the hybrid fins comprises a dielectric fin and a dielectricstructure over the dielectric fin. At step 1030, a gate structure isformed over the semiconductor fins and over the hybrid fins. At step1040, first portions of the patterned mask layer, first portions of theepitaxial layers, and first portions of the dielectric structures thatare disposed beyond sidewalls of the gate structure are removed withoutsubstantially removing the dielectric fins. At step 1050, an interlayerdielectric (ILD) layer is formed over the dielectric fins and around thegate structure. At step 1060, a gate electrode of the gate structure isremoved to form an opening in the gate structure, the opening exposingsecond portions of the patterned mask layer and second portions of thedielectric structure that are disposed under the gate structure. At step1070, a first dielectric structure of the dielectric structures isremoved while keeping a second dielectric structure of the dielectricstructures. At step 1080, the first semiconductor material isselectively removed, where after the selectively removing, the secondsemiconductor material forms nanowires, where the second dielectricstructure extends further from the substrate than an uppermost surfaceof the nanowires.

Embodiments may achieve advantages. For example, the dielectric fin 116has a larger width T₂ under the source/drain regions 133 and a smallerwidth T₁ under the gate electrode 143. The larger width T₂ provideshigher error tolerance for the photolithography and etching process toform contact openings and helps to reduce electrical short betweenadjacent source/drain regions 133. The smaller width T₁ makes it easierfor the fill metal to fill the recess between gate spacers 129 to formthe gate electrode 143, thereby improving production yield and reducingthe electrical resistance of the gate electrode. In addition, thedielectric fins 116 improve the time dependent dielectric breakdown(TDDB) performance of the device formed. Furthermore, separation of thedifferent metal gates (e.g., 145A, 145B, 145C) is achieved by thedielectric structures 118 in a self-aligned manner. While the presentdisclosure is discussed in the context of GAA FET devices (e.g.,nanowire devices), the principle of the disclosure may be applied toother types of devices, such as nanosheet devices or Fin Field-Effect(FinFET) devices.

In accordance with an embodiment, a method of forming a semiconductordevice includes forming semiconductor fins over a substrate and apatterned mask layer over the semiconductor fins, wherein thesemiconductor fins comprise epitaxial layers over semiconductor strips,wherein the epitaxial layers comprise alternating layers of a firstsemiconductor material and a second semiconductor material; forminghybrid fins over isolation regions on opposing sides of thesemiconductor fins, wherein each of the hybrid fins comprises adielectric fin and a dielectric structure over the dielectric fin;forming a gate structure over the semiconductor fins and over the hybridfins; removing first portions of the patterned mask layer, firstportions of the epitaxial layers, and first portions of the dielectricstructures that are disposed beyond sidewalls of the gate structurewithout substantially removing the dielectric fins; forming aninterlayer dielectric (ILD) layer over the dielectric fins and aroundthe gate structure; removing a gate electrode of the gate structure toform an opening in the gate structure, the opening exposing secondportions of the patterned mask layer and second portions of thedielectric structure that are disposed under the gate structure;removing a first dielectric structure of the dielectric structures whilekeeping a second dielectric structure of the dielectric structures; andselectively removing the first semiconductor material, wherein after theselectively removing, the second semiconductor material forms nanowires,wherein the second dielectric structure extends further from thesubstrate than an uppermost surface of the nanowires. In an embodiment,the method further includes fill the opening with an electricallyconductive material; and recessing an upper surface of the electricallyconductive material below an upper surface of the second dielectricstructure. In an embodiment, the method further includes forming a gatedielectric material around the nanowires before filling the opening. Inan embodiment, the method further includes, before filling the opening,removing at least upper layers of the second portions of the patternedmask layer exposed by the opening. In an embodiment, the method furtherincludes, after selectively removing the first semiconductor materialand before filling the opening, reducing first widths of first portionsof the dielectric fins disposed under the gate structure while keepingsecond widths of second portions of the dielectric fins disposed beyondsidewalls of the gate structure unchanged. In an embodiment, the methodfurther includes forming a tungsten layer on the electrically conductivematerial after the recessing. In an embodiment, removing first portionsof the patterned mask layer, first portions of the epitaxial layers, andfirst portions of the dielectric structures comprises performing ananisotropic etching using the gate structure as an etching mask. In anembodiment, the method further includes, before forming the hybrid fins,forming a capping layer comprising the first semiconductor materialalong sidewalls of the epitaxial layers and along sidewalls of thepatterned mask layer, wherein the hybrid fins are formed to contact thecapping layer. In an embodiment, the dielectric fin is formed of one ormore dielectric materials with a first dielectric constant, and thedielectric structure is formed of one or more dielectric materials witha second dielectric constant larger than the first dielectric constant.In an embodiment, the method further includes forming source/drainregions over the semiconductor strips after removing the first portionsof the patterned mask layer, the first portions of the epitaxial layers,and the first portions of the dielectric structures and before formingthe ILD layer. In an embodiment, the method further includes, afterremoving the first portions of the patterned mask layer, the firstportions of the epitaxial layers, and the first portions of thedielectric structures and before forming the source/drain regions,replacing the first semiconductor material disposed under gate spacersof the gate structure with a first dielectric material. In anembodiment, the replacing includes: performing a lateral etch process toremove the first semiconductor material disposed under the gate spacers;and filling spaces left by the removal of the first semiconductormaterial using the first dielectric material.

In accordance with an embodiment, a method of forming a semiconductordevice includes forming semiconductor strips protruding above asubstrate; forming isolation regions between adjacent ones of thesemiconductor strips; forming hybrid fins on the isolation regions, thehybrid fins comprising dielectric fins and dielectric structures overthe dielectric fins; forming a dummy gate structure over thesemiconductor strips and the hybrid fins; forming source/drain regionsover the semiconductor strips and on opposing sides of the dummy gatestructure; forming nanowires under the dummy gate structure, wherein thenanowires are over and aligned with respective semiconductor strips, andthe source/drain regions are at opposing ends of the nanowires, whereinthe hybrid fins extend further from the substrate than the nanowires;after forming the nanowires, reducing widths of center portions of thehybrid fins while keeping widths of end portions of the hybrid finsunchanged, wherein the center portions of the hybrid fins are under thedummy gate structure, and the end portions of the hybrid fins are beyondboundaries of the dummy gate structure; and forming an electricallyconductive material around the nanowires. In an embodiment, forming thenanowires includes: before forming the dummy gate structure, formingalternating layers of a first semiconductor material and a secondsemiconductor material over the semiconductor strips; after forming thedummy gate structure, removing the first semiconductor material and thesecond semiconductor material that are disposed beyond the boundaries ofthe dummy gate structure; forming an interlayer dielectric layer overthe source/drain regions and around the dummy gate structure; afterforming the interlayer dielectric layer, removing a gate electrode ofthe dummy gate structure to form an opening in the dummy gate structure,the opening exposing the first semiconductor material disposed under thedummy gate structure; and selectively removing the first semiconductormaterial disposed under the dummy gate structure. In an embodiment,forming the nanowires further includes: before forming the dummy gatestructure, forming a capping layer between the hybrid fins and thealternating layers of the first semiconductor material and the secondsemiconductor material, the capping layer formed using the firstsemiconductor material. In an embodiment, the method further includes:after removing the first semiconductor material and the secondsemiconductor material that are disposed beyond the boundaries of thedummy gate structure, recessing the first semiconductor material fromsidewalls of remaining portions of the second semiconductor material;and filling a space left by the recessing of the first semiconductormaterial with a dielectric material. In an embodiment, the methodfurther includes recessing an upper surface of the electricallyconductive material below upper surfaces of the dielectric structures.In an embodiment, the method further includes forming a gate dielectricmaterial around the nanowires before forming the electrically conductivematerial.

In accordance with an embodiment, a semiconductor device includes: asemiconductor strip protruding above a substrate; a first isolationregion and a second isolation region on opposing sides of thesemiconductor strip; nanowires over and aligned with the semiconductorstrip; source/drain regions at opposing ends of the nanowires; a firstdielectric fin on the first isolation region; and a metal gate aroundthe nanowires and around center portions of the first dielectric fin,wherein end portions of the first dielectric fin are disposed onopposing sides of the metal gate, wherein the end portions of the firstdielectric fin are wider than the center portions of the firstdielectric fin. In an embodiment, the semiconductor device furtherincludes a first dielectric structure over the first dielectric fin,wherein the first dielectric structure extends above an upper surface ofthe metal gate distal to the substrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: forming semiconductor fins over a substrate and apatterned mask layer over the semiconductor fins, wherein thesemiconductor fins comprise epitaxial layers over semiconductor strips,wherein the epitaxial layers comprise alternating layers of a firstsemiconductor material and a second semiconductor material; forminghybrid fins over isolation regions on opposing sides of thesemiconductor fins, wherein each of the hybrid fins comprises adielectric fin and a dielectric structure over the dielectric fin;forming a gate structure over the semiconductor fins and over the hybridfins; removing first portions of the patterned mask layer, firstportions of the epitaxial layers, and first portions of the dielectricstructures that are disposed beyond sidewalls of the gate structurewithout substantially removing the dielectric fins; forming aninterlayer dielectric (ILD) layer over the dielectric fins and aroundthe gate structure; removing a gate electrode of the gate structure toform an opening in the gate structure, the opening exposing secondportions of the patterned mask layer and second portions of thedielectric structure that are disposed under the gate structure;removing a first dielectric structure of the dielectric structures whilekeeping a second dielectric structure of the dielectric structures; andselectively removing the first semiconductor material, wherein after theselectively removing, the second semiconductor material forms nanowires,wherein the second dielectric structure extends further from thesubstrate than an uppermost surface of the nanowires.
 2. The method ofclaim 1, further comprising: fill the opening with an electricallyconductive material; and recessing an upper surface of the electricallyconductive material below an upper surface of the second dielectricstructure.
 3. The method of claim 2, further comprising forming a gatedielectric material around the nanowires before filling the opening. 4.The method of claim 2, further comprising, before filling the opening,removing at least upper layers of the second portions of the patternedmask layer exposed by the opening.
 5. The method of claim 2, furthercomprising, after selectively removing the first semiconductor materialand before filling the opening, reducing first widths of first portionsof the dielectric fins disposed under the gate structure while keepingsecond widths of second portions of the dielectric fins disposed beyondsidewalls of the gate structure unchanged.
 6. The method of claim 2,further comprising forming a tungsten layer on the electricallyconductive material after the recessing.
 7. The method of claim 1,wherein removing first portions of the patterned mask layer, firstportions of the epitaxial layers, and first portions of the dielectricstructures comprises performing an anisotropic etching using the gatestructure as an etching mask.
 8. The method of claim 1, furthercomprising, before forming the hybrid fins, forming a capping layercomprising the first semiconductor material along sidewalls of theepitaxial layers and along sidewalls of the patterned mask layer,wherein the hybrid fins are formed to contact the capping layer.
 9. Themethod of claim 1, wherein the dielectric fin is formed of one or moredielectric materials with a first dielectric constant, and thedielectric structure is formed of one or more dielectric materials witha second dielectric constant larger than the first dielectric constant.10. The method of claim 1, further comprising forming source/drainregions over the semiconductor strips after removing the first portionsof the patterned mask layer, the first portions of the epitaxial layers,and the first portions of the dielectric structures and before formingthe ILD layer.
 11. The method of claim 10, further comprising, afterremoving the first portions of the patterned mask layer, the firstportions of the epitaxial layers, and the first portions of thedielectric structures and before forming the source/drain regions,replacing the first semiconductor material disposed under gate spacersof the gate structure with a first dielectric material.
 12. The methodof claim ii, wherein the replacing comprises: performing a lateral etchprocess to remove the first semiconductor material disposed under thegate spacers; and filling spaces left by the removal of the firstsemiconductor material using the first dielectric material.
 13. A methodof forming a semiconductor device, the method comprising: formingsemiconductor strips protruding above a substrate; forming isolationregions between adjacent ones of the semiconductor strips; forminghybrid fins on the isolation regions, the hybrid fins comprisingdielectric fins and dielectric structures over the dielectric fins;forming a dummy gate structure over the semiconductor strips and thehybrid fins; forming source/drain regions over the semiconductor stripsand on opposing sides of the dummy gate structure; forming nanowiresunder the dummy gate structure, wherein the nanowires are over andaligned with respective semiconductor strips, and the source/drainregions are at opposing ends of the nanowires, wherein the hybrid finsextend further from the substrate than the nanowires; after forming thenanowires, reducing widths of center portions of the hybrid fins whilekeeping widths of end portions of the hybrid fins unchanged, wherein thecenter portions of the hybrid fins are under the dummy gate structure,and the end portions of the hybrid fins are beyond boundaries of thedummy gate structure; and forming an electrically conductive materialaround the nanowires.
 14. The method of claim 13, wherein forming thenanowires comprises: before forming the dummy gate structure, formingalternating layers of a first semiconductor material and a secondsemiconductor material over the semiconductor strips; after forming thedummy gate structure, removing the first semiconductor material and thesecond semiconductor material that are disposed beyond the boundaries ofthe dummy gate structure; forming an interlayer dielectric layer overthe source/drain regions and around the dummy gate structure; afterforming the interlayer dielectric layer, removing a gate electrode ofthe dummy gate structure to form an opening in the dummy gate structure,the opening exposing the first semiconductor material disposed under thedummy gate structure; and selectively removing the first semiconductormaterial disposed under the dummy gate structure.
 15. The method ofclaim 14, wherein forming the nanowires further comprises: beforeforming the dummy gate structure, forming a capping layer between thehybrid fins and the alternating layers of the first semiconductormaterial and the second semiconductor material, the capping layer formedusing the first semiconductor material.
 16. The method of claim 15,further comprising: after removing the first semiconductor material andthe second semiconductor material that are disposed beyond theboundaries of the dummy gate structure, recessing the firstsemiconductor material from sidewalls of remaining portions of thesecond semiconductor material; and filling a space left by the recessingof the first semiconductor material with a dielectric material.
 17. Themethod of claim 13, further comprising recessing an upper surface of theelectrically conductive material below upper surfaces of the dielectricstructures.
 18. The method of claim 13, further comprising forming agate dielectric material around the nanowires before forming theelectrically conductive material.
 19. A semiconductor device comprising:a semiconductor strip protruding above a substrate; a first isolationregion and a second isolation region on opposing sides of thesemiconductor strip; nanowires over and aligned with the semiconductorstrip; source/drain regions at opposing ends of the nanowires; a firstdielectric fin on the first isolation region; and a metal gate aroundthe nanowires and around a center portion of the first dielectric fin,wherein the center portion of the first dielectric fin is disposedbetween a lower surface of the metal gate and the substrate, wherein thelower surface of the metal gate faces the substrate and physicallycontacts the center portion of the first dielectric fin, wherein endportions of the first dielectric fin are disposed on opposing sides ofthe metal gate, wherein the end portions of the first dielectric fin arewider than the center portion of the first dielectric fin.
 20. Thesemiconductor device of claim 19, further comprising a first dielectricstructure over the first dielectric fin, wherein the first dielectricstructure extends above an upper surface of the metal gate distal to thesubstrate.